Method for depositing a flattened droplet on a surface and apparatus therefor, and a pump therefor

ABSTRACT

A method and apparatus therefor for depositing a flattened droplet on a partially absorbent surface comprising the steps of providing a narrow bore transfer tube having a proximal end and a distal end and containing a microvolume of liquid, the proximal end connected to a pneumatic system adapted for issuing an outgoing flow of displacement gas into the tube and drawing an incoming flow of displacement gas therefrom; and issuing an outgoing flow of displacement gas for slowly discharging substantially the entire microvolume of liquid as a droplet on the surface and controllably blowing one or more bubbles into the droplet towards the end of its discharge for flattening the droplet on the surface. A pump ( 31 ) comprising a housing ( 33 ) having a bore ( 34 ) with an internal peripheral surface ( 36 ), and a stationary annular sealing member ( 48 ) integrally formed therewith at a first end ( 37 ) of a pair of opposite ends ( 37  and  38 ); a slide rod ( 39 ) disposed in the bore and having an external peripheral surface ( 41 ) and a displaceable annular sealing member ( 49 ) integrally formed therewith; the sealing members sealing the peripheral surfaces to define a vented displacement volume ( 51 ) therebetween whose volume is proportional to an annular cross section area between the peripheral surfaces and a distance between the sealing members; and the slide rod being slidably reciprocable between first and second positions respectively toward and away from the stationary sealing member whereupon the displaceable sealing member moves to reduce the volume to issue an outgoing flow of displacement gas from the displacement volume on a downstroke of the slide rod from its second position to its first position and the displaceable sealing member moves to increase the volume to draw an incoming flow of displacement gas into the displacement volume on an upstroke of the slide rod from its first position to its position.

FIELD OF THE INVENTION

[0001] The invention relates to a method for depositing a flatteneddroplet on a surface suitable for in vitro fertilization (IVF) andembryo transfer (ET), and apparatus therefor, and a pump therefor.

BACKGROUND OF THE INVENTION

[0002] In an IVF-ET procedure, oocytes are aspirated from female ovariesand inseminated in vitro with male sperm in a culture medium to formembryos which are incubated prior to their being transferred to asubject by means of a two-stage transfer procedure. The transferprocedure includes the aspiration of a relatively large volume of about20-40 μl of culture medium containing between one to five embryos into atransfer catheter by means of a manually operated syringe and itssubsequent injection into a subject.

[0003] Since a conventional IVF-ET procedure is manual, the rate ofinjection of the embryo containing culture into a uterine cavity mayvary significantly. Thus, on the one hand, too slow an injection ratemay cause embryo containing culture medium to trickle down the transfercatheter's outer surface and, on the other hand, too quick an injectionrate may severely damage embryo(s) following their collision against auterine wall. The latter case may also flood a subject's uterus possiblyresulting in a failed procedure as embryos are either washed out of heruterus or implanted in one of her Fallopian tubes leading to an ectopicpregnancy. Another disadvantage attendant with the use of a relativelylarge volume of culture medium is that it may alter the specificproperties of the micro-environment within a subject's uterus requiredfor successful embryo implantation and its normal development.

[0004] The present invention is based on the notion that substantiallyautomating embryo implantation in IVF-ET procedures may overcome some ofthe shortcomings of the conventional IVF-ET procedure.

SUMMARY OF THE INVENTION

[0005] In accordance with the present invention, there is provided amethod for depositing a flattened droplet on a surface particularlysuitable for depositing embryo(s) containing culture medium at a desiredsite in a uterus cavity, and apparatus therefor, and a pump therefor.

[0006] In accordance with a first aspect of the invention, there isprovided a method for depositing a flattened droplet on a partiallyabsorbent surface, the method comprising the steps of:

[0007] (a) providing a narrow bore transfer tube having a proximal endand a distal end and containing a microvolume of liquid, the proximalend connected to a pneumatic system for issuing an outgoing flow ofdisplacement gas into the transfer tube and drawing an incoming flow ofdisplacement gas thereinto from the transfer tube; and

[0008] (b) issuing an outgoing flow of displacement gas for slowlydischarging substantially the entire microvolume of liquid as a dropleton the surface and controllably blowing one or more bubbles into thedroplet towards the end of its discharge to flatten the droplet on thesurface.

[0009] A “flattened droplet” in the context of the present invention canbe demonstrated on standard 80 gram/m² A4 paper for use with ink jetprinters, such paper constituting a partially absorbent surface on whicha flattened droplet of the present invention has a projected surfacearea about three to six times larger than that of a naturally formingdome-like droplet. A “partially absorbent surface” in the context of thepresent invention is one which absorbs a relatively insignificant volumeof a naturally forming dome-like droplet over about 60 seconds. Theflattening of a droplet as achieved by the method of the presentinvention is not by the relatively slow process of its being absorbedassuming it does not dry but rather as a consequence of its beingeffectively inflated by one or more bubbles of displacement gascontrollably blown thereinto towards the end of its discharge whichtypically occurs over 5-20 seconds from an initial outward displacementof the microvolume of liquid. The surface may be flat, inclined or eveninverted and still maintain the droplet in its flattened shape by virtueof the prevailing surface tension therewith.

[0010] A “microvolume of liquid” in the context of the present inventionis a volume of liquid in the microliter range, e.g., within the range of0.05-5 μl, preferably within the range of 0.1-3.0 μl, and particularlywithin the range of 0.3-2.0 μl. In the case of an IVF-ET procedure on ahuman subject when the catheter is upwardly inclined, even though thedischarge of culture medium is relatively slow, its volume is so smallso as to avoid a downward trickle along the catheter's outer surface.

[0011] In accordance with a preferred embodiment of the presentinvention, step (a) includes:

[0012] (a1) preventing capillary forces to draw liquid into the transfertube upon insertion of its distal end into a vessel containing liquid;

[0013] (a2) inserting the transfer tube's distal end into the liquid;

[0014] (a3) drawing an incoming flow of displacement gas from thetransfer tube such that a microvolume of liquid is drawn thereinto; and

[0015] (a4) removing the transfer tube's distal end from the liquid.

[0016] The step of preventing capillary forces is preferably achieved byissuing an outgoing flow of displacement gas into the transfer tube soas to create a positive pressure therein. Alternatively, this step canbe achieved, for example, by providing a seal at its distal end. Afterthe transfer tube's distal end is removed from the liquid, themicrovolume of liquid is preferably inwardly drawn away from its distalend as a safety precaution whereafter the inward displacement isneutralized by a brief outgoing flow of displacement gas into thetransfer tube.

[0017] After the discharge of the microvolume of liquid from thetransfer tube, the flattened droplet in most cases is still connected tothe transfer tube's distal end and therefore to prevent its suction backinto the transfer tube, the outgoing flow of displacement gas ismaintained until the droplet is disconnected from the transfer tube'sdistal end by manually withdrawing the transfer tube. This outgoing flowof displacement gas may also remove any small quantities of themicrovolume which were not initially discharged and which may include anembryo(s) in an IVF-ET procedure.

[0018] In accordance with a second aspect of the present invention,there is provided apparatus for depositing a flattened droplet of liquidon a partially absorbent surface, the apparatus for use with a narrowbore transfer tube having a proximal end and a distal end and a vesselof liquid, the apparatus comprising:

[0019] (a) a pneumatic system connected to the transfer tube's proximalend and adapted for issuing an outgoing flow of displacement gas intosaid transfer tube and drawing an incoming flow of displacement gasthereinto from said transfer tube; and

[0020] (b) a control mechanism for controlling said pneumatic system indifferent operational modes including:

[0021] a user controlled suction mode for drawing an incoming flow ofdisplacement gas from the transfer tube whereby a microvolume of liquidis drawn thereinto prior to the removal of said distal end from thevessel; and

[0022] a user initiated automated delivery mode for issuing an outgoingflow of displacement gas into the transfer tube for slowly dischargingsubstantially the entire microvolume of liquid as a droplet on thesurface and controllably blowing one or more bubbles into the droplettowards the end of its discharge to flatten the droplet on the surface.

[0023] In accordance with a third aspect of the present invention, thereis provided a pump comprising a housing having a bore with an internalperipheral surface, and a stationary annular sealing member integrallyformed therewith at a first end of a pair of opposite ends; a slide roddisposed in said bore and having an external peripheral surface and adisplaceable annular sealing member integrally formed therewith; saidsealing members sealing said peripheral surfaces to define a venteddisplacement volume therebetween whose volume is proportional to anannular cross section area between said peripheral surfaces and adistance between said sealing members; and said slide rod being slidablyreciprocable between first and second positions respectively toward andaway from said stationary sealing member whereupon said displaceablesealing member moves to reduce said volume to issue an outgoing flow ofdisplacement gas from said displacement volume on a downstroke of saidslide rod from said second position to said first position and saiddisplaceable sealing member moves to increase said volume to draw anincoming flow of displacement gas into said displacement volume on anupstroke of said slide rod from said first position to said secondposition.

[0024] Preferably both the bore and the slide rod are of a rightcylindrical shape such that the displacement volume has a crosssectional area defined by π(a²-b²) where a and b are the radii of thebore's internal peripheral surface and the slide rod's externalperipheral surface, respectively. Preferably, the cross section area isin the order of 4-10 mm² and the pump has a displacement volumeincrementally changeable in the order of 0.1-0.4 μl.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to understand the invention and how it is used, apreferred embodiment will now be described by way of a non-limitingexample only, with reference to the accompanying drawings in which:

[0026]FIG. 1 is a pictorial view of apparatus for depositing a flatteneddroplet on a surface in accordance with the present invention;

[0027] FIGS. 2A-2L illustrates operation of the apparatus of FIG. 1 fordepositing the flattened droplet on the surface;

[0028]FIG. 3 is a pictorial view of a pump in accordance with thepresent invention; and

[0029]FIGS. 4 and 5 are cross sectional views of the pump of FIG. 3along lines A-A and B-B in FIG. 3, respectively.

DETAILED DESCRIPTION OF THE DRAWINGS

[0030] With reference now to FIGS. 1 and 2, apparatus 1 is employed fordepositing a flattened droplet F on a partially absorbent surface S, forexample, on a subject's endometrium in an IVF-ET procedure. Apparatus 1includes a suction control unit 2 normally permanent located in alaboratory for the preparation of an embryo carrying catheter 3constituting a transfer tube, a transfer control unit 4 normallypermanently located in a treatment room where an IVF-ET procedure iscarried out and a portable casing 6 for consecutive connection to thesuction control unit 2 and the transfer control unit 4 by means ofconnectors 7 and 8. The casing 6 includes a pneumatic system 9 which ispermanently connected to the catheter 3 during an entire IVF-ETprocedure via suitable air tubing 11 and an air filter 12. The casing 6also has a receptacle 13 for accommodating the catheter 3 during itstransport from the laboratory to the treatment room.

[0031] The pneumatic system 9 is under a control mechanism 14 includinga computer mouse 16 for controlling the suction control unit 2 forinitiating a user controlled suction mode to prepare the catheter 3 witha microvolume of embryo containing culture medium and a foot pedal 17for controlling the transfer control unit 4 for initiating a userinitiated automated delivery mode for depositing the flattened droplet Fon the surface S. The computer mouse 16 has an upstroke control 18 fordrawing an incoming flow of displacement gas into the pneumatic system 9from the catheter 3, a downstroke control 19 for issuing an outgoingflow of displacement gas from the pneumatic system 9 into the catheter 3and optionally a speed control 21 for controlling the flow rate of thedisplacement gas either from or into the pneumatic system 9. The suctioncontrol unit 2 is also provided with a reset button 22 for priming thepneumatic system 9 for a pre-suction mode of issuing an outgoing flow ofdisplacement gas as indicated by a READY indicator light 23 prior to thepreparation of the catheter 3. The different stages of the automaticdelivery mode are indicated by a READY indicator light 24, a GOindicator light 26 and a DONE indicator light 27.

[0032] In operation, the casing 6 is initially connected to the suctioncontrol unit 2 and the catheter 3 is connected to the pneumatic system 9via the air tubing 11 and the filter 12. An operator presses the resetbutton 22 whereupon a lit READY indicator light 23 indicates an outgoingflow of displacement gas creating a positive pressure within catheter 3to prevent capillary forces drawing culture medium thereinto uponinsertion of its distal end 3A into a vessel of culture medium Ccontaining embryos E shown exaggerated in all FIGS. 2A-2L (see FIG. 2A).The operator inserts the distal end 3A into the vessel of culture mediumC for aspirating about 0.3 to 0.6 μl microvolume of culture mediumcontaining an embryo E into the catheter 3 (see FIG. 2B). Once an embryois clearly seen to be close to the catheter's distal end 3A, the rate ofaspiration of culture medium may be increased by depressing the speedcontrol 21. If a single embryo is to be transferred, distal end 3A isthen be removed from the culture medium otherwise additional embryos maybe captured as shown.

[0033] Once the catheter 3 contains one or more embryos, the operatorwithdraws its distal end 3A from the culture medium and then proceeds todepress the downstroke control 19 to slowly displace the microvolume ofculture medium inwardly (see FIG. 2C). After the microvolume of culturemedium has been inwardly displaced by about 5-15 mm from the catheter'sdistal end 3A, its motion is arrested by a momentary outgoing flow ofdisplacement gas (see FIG. 2D) so that it finally comes to rest at adistance of about 10 mm (see FIG. 2E) therefrom thereby ensuring that itcannot be inadvertently lost during transportation of the casing 6between the laboratory and the treatment room. The catheter 3 is thenplaced in the receptacle 13 (see FIG. 1) during the transportation ofthe casing 6 from the laboratory to the treatment room.

[0034] For transfer of the embryos E onto the surface S, the catheter 3is laid on the surface S (see FIG. 2F) whereupon a first depression onthe foot pedal 17 causes the READY indicator light 24 to be litindicating that the automatic delivery mode can be initiated.Thereafter, a second depression on the foot pedal 17 causes the GOindicator light 26 to be lit indicating that an outgoing flow ofdisplacement gas is displacing the microvolume of culture medium towardsthe catheter's distal end 3A (see FIG. 2G). The outgoing flow ofdisplacement gas causes a concave shaped meniscus to be slowly formedwhich increases in size until it suddenly ruptures whereby most of themicrovolume of culture medium is discharged as a droplet D on thesurface S (see FIGS. 2H and 2J). The discharge is accompanied by one ormore air bubbles B for effectively inflating the droplet D therebyconsiderably widening its projected surface area on the surface S toform the flattened droplet F whose shape is maintained by its prevailingsurface tension with the surface S (see FIG. 2K).

[0035] The GO indicator light 26 is then extinguished indicating thatthe operator should slightly withdraw the catheter 3 so as to detach itfrom the droplet F whilst at the same time there is an outgoing flow ofdisplacement gas (see FIG. 2L). In the case of an actual IVF-ETprocedure, withdrawal is limited to between about 10-15 mm such that thecatheter's distal end 3A still lies along a subject's endometrium.Finally, a further outgoing flow of additional displacement gas isprovided so as to remove any culture medium which may remain in thecatheter 3. The DONE indicator light 27 is then lit to indicate that thecatheter 3 can be completely removed.

[0036] With reference now to FIGS. 3-5, a pump 31 constituting apneumatic system for use with the apparatus 1 includes a base 32 with ahousing 33 having a longitudinal right cylindrical throughbore 34 withan internal peripheral surface 36 of a radius a and having first andsecond opposite ends 37 and 38. A right cylindrical slide rod 39 with anexternal peripheral surface 41 of a radius b and first and secondopposite end 42 and 43 is disposed in the bore 34 and is slidinglyreciprocated by means of a linear actuator screw 44 driven by a stepmotor 46.

[0037] A sleeve bearing 47 having a sealing O-ring gasket 48constituting a stationary annular sealing member is disposed at thefirst end 37 and an O-ring gasket 49 constituting a displaceable annularsealing member is disposed at the slide rod end 42, the gaskets 48 and49 sealingly the peripheral surfaces 36 and 41 to define a displacementvolume 51 vented by a vent 52. The displacement volume 51 has a volumeequal to a product of a cross sectional area between the surface 36 and41 defined by π(a²-b²) and the distance between the gaskets 48 and 49.

[0038] The slide rod 39 is slidingly reciprocable between first andsecond positions respectively toward and away from the gasket 48whereupon the displacement volume 51 has a minimum value when thegaskets 48 and 49 are adjacent in which case a major portion of theslide rod 39 is exterior to the bore 34 and a maximum value when thegaskets 48 and 49 are remote from one another. In operation, the gasket49 moves to reduce the volume of the displacement volume 51 to issue anoutgoing flow of displacement gas therefrom on a downstroke of the sliderod 39 from its second position to its first position and the gasket 49moves to increase the volume of the displacement volume 51 to draw anincoming flow of displacement gas thereinto on an upstroke of the sliderod 39 from its first position to its second position.

[0039] The bore 34 and the slide rod 39 typically have diameters in therange of about 5-10 mm and which differ in the range of about 0.3-0.7 mmsuch that the cross section area is in the order of about 4-10 mm². Thethreading on actuator screw 44 is designed such that each step of themotor 45 causes an incremental movement of the slide rod 39 of about0.001-0.002 inches. The motor 45 is typically driven at a rate of about20-300 steps per second.

[0040] Various modifications and changes may be made in theconfiguration described above that come within the spirit of theinvention. The invention embraces all such changes and modificationscoming within the scope of the appended claims.

1. A method for depositing a flattened droplet on a partially absorbent surface comprising the steps of: (a) providing a narrow bore transfer tube having a proximal end and a distal end and containing a microvolume of liquid, the proximal end connected to a pneumatic system adapted for issuing an outgoing flow of displacement gas into the tube and drawing an incoming flow of displacement gas therefrom; and (b) issuing an outgoing flow of displacement gas for slowly discharging substantially the entire microvolume of liquid as a droplet on the surface and controllably blowing one or more bubbles into the droplet towards the end of its discharge for flattening the droplet on the surface.
 2. The method of claim 1 wherein step (a) includes: (a1) preventing capillary forces to draw liquid into the transfer tube upon the insertion of its distal end into a vessel containing liquid; (a2) inserting the transfer tube's distal end into the vessel; (a3) drawing an incoming flow of displacement gas from the transfer tube such that a microvolume of liquid is drawn thereinto; and (a4) removing the transfer tube's distal end from the liquid.
 3. The method of claim 2 wherein step (a1) includes issuing an outgoing flow of displacement gas into the transfer tube.
 4. The method of claim 3 further comprising the step of: (a5) drawing the microvolume of liquid into the transfer tube away from its distal end; and (a6) neutralizing the inward displacement by a brief outgoing flow of displacement gas into the transfer tube.
 5. The method according to any one of claims 1-4 further comprising the step of: (c) providing additional outflow of displacement gas while displacing the transfer tube away from the droplet so separate the droplet from its distal end.
 6. The method according to any one of claims 1-5 wherein the microvolume of liquid is a culture medium containing embryo(s) which are urged against the surface by the droplet's prevailing surface tension.
 7. Apparatus for depositing a flattened droplet on a partially absorbent surface, the apparatus for use with a narrow bore transfer tube having a proximal end and a distal end and a vessel of liquid, the apparatus comprising: (a) a pneumatic system connected to the transfer tube's proximal end and adapted for issuing an outgoing flow of displacement gas into said transfer tube and drawing an incoming flow of displacement gas thereinto from said transfer tube; and (b) a control mechanism for controlling said pneumatic system in different operational modes including: an user controlled suction mode for drawing an incoming flow of displacement gas from said transfer tube whereby a microvolume of liquid is drawn thereinto prior to the removal of said distal end from the vessel; and an user initiated automated delivery mode for issuing an outgoing flow of displacement gas into said transfer tube for slowly discharging substantially the entire microvolume of liquid as a droplet on the surface and controllably blowing one or more bubbles into the droplet towards the end of its discharge for flattening the droplet on the surface.
 8. Apparatus according to claim 7 wherein said control mechanism includes an automatic pre-suction mode for issuing an outgoing flow of displacement gas.
 9. Apparatus according to claim 7 or 8 wherein separate units house a suction control unit for controlling said user controlled suction mode and a transfer control unit for controlling said user initiated automatic delivery mode.
 10. A pump comprising a housing having a bore with an internal peripheral surface, and a stationary annular sealing member integrally formed therewith at a first end of a pair of opposite ends; a slide rod disposed in said bore and having an external peripheral surface and a displaceable annular sealing member integrally formed therewith; said sealing members sealing said peripheral surfaces to define a vented displacement volume therebetween whose volume is proportional to an annular cross section area between said peripheral surfaces and a distance between said sealing members; and said slide rod being slidably reciprocable between first and second positions respectively toward and away from said stationary sealing member whereupon said displaceable sealing member moves to reduce said volume to issue an outgoing flow of displacement gas from said displacement volume on a downstroke of said slide rod from said second position to said first position and said displaceable sealing member moves to increase said volume to draw an incoming flow of displacement gas into said displacement volume on an upstroke of said slide rod from said first position to said second position.
 11. The pump according to claim 10 wherein both said bore and said slide rod are of right cylindrical shape and said cross section area is defined by π(a²-b²) where a and b are the radii of said internal peripheral surface and said external peripheral surface, respectively.
 12. The pump according to either claim 10 or 11 wherein said cross section area has an area of about 4-10 mm².
 13. The pump according to any one of claims 10-12 wherein said displacement volume can be incrementally changed in the order of 0.1-0.4 μl. 